- The side slope of the canal depends upon the type of soil.
- The canals in alluvial soils are designed assuming a 1/2 :1 side slope, irrespective of the actual initial side slope.
- It is assumed that after the due course of a run, the canal section would ultimately acquire a 1/2: 1 slope.
- This happens because silt gets deposited on the berms.
- Had section been designed with 1/2: 1 slope initially, the section
- would be reduced in due course of time due to silting and the section remaining would be inadequate.
- As per the recommendation of the Central Water.
- Power Commission (C.W.P.C.) the side slopes for various soils should be given in Table 19.2.
- It is a narrow strip of land, left on either side of a channel at G.L., between upper edge of the cut and the inside toe of the bank.
- The width of the berm depends upon the size of the channel.
- If canal is in partial cutting, the original width of the berm will be small but it becomes wider after silting over.
- The berms and side slopes.
- The canals while constructing area excavated with 1: 1 slope, but after a run, for few months.
The section automatically acquires a side slope of 1/2: 1.
Berm performs the following functions.
- The width of the canal can be easily increased if required.
- Slipping soils and boulders are held up at berms and do not allow them to be dropped into the channel.
- It acts as a storage space for materials if some repair or construction work is to be clone in the canal.
- Barrow pits may be made on banks for taking soil.
- These berms get silted up very soon.
- Such a need for barrow pits arises during canal breaches.
- They strengthen the channel banks.
- The rise in water level is marginal with a substantial increase in discharge above the full capacity of the canal.
- If by mistake excess discharge enters the canal, they do not allow water to rise much and thus a possible breach of the canal is averted.
- Because of silting of inside edge and top, the terms become impervious, and as such, loss of water by seepage is reduced.
- Waves developed in the canal do not come in direct contact with the banks and hence possibilities of bank erosion are reduced.
- They also provide an easy path for inspection.
- They increase the width of the bank, and thus, the seepage line is not likely to be exposed.
- For channels in full cutting, a berm of width equal to depth of water is provided at 50 cm above the F.S.L.
- In channels, partly in cutting, the berm provided is such that after silting its width at F.S.L.
- Will not exceed twice the depth of water.
- In channels, fully in an embankment, a berm width varying from twice the depth to thrice the depth is provided at F.S.L.
- The minimum berm width can also be found out from the Table 19.3.